Detent mechanism



Feb. 2, 1965 D. c. DURGIN 3,

DETENT MECHANISM Filed April 10, 1962 F l G.

' DOUGLAS- C. DURGIN fl/ ATTGRNEY United States Patent 3,167,972 DETENT MECHANISM Douglas C. Durgin, West Orange, N.J., assignor to Monroe International Corporation, a corporation of Delaware Filed Apr. 10, 1962, Ser. No. 186,510 Claims. (Ci. 74527) The present invention relates to detent mechanism and more particularly to such mechanism for accurately locating an adjustable machine part in any one of a plurality of closely spaced operating positions.

Detent mechanism usually includes a member such as a toothed wheel or rack, the tooth spaces of which correspond respectively to the positions to which the machine part may be adjusted. As the part is adjusted to its successive positions, a spring urged pawl or detent arm engages the corresponding tooth spaces to locate the part.

Obviously, detent mechanism of the above type must be made to closer tolerances and is less positive in operation when closely spaced detent teeth are employed for corresponding closely spaced positions in which the machine part may be located. Furthermore, if the machine part is adjustable in both directions, the pawl end engaging the detent teeth would preferably be in the form of a roller or would be rounded to permit camming action on the spring urged pawl as it is moved to its successive positions. Consequently if the part is adjusted manually, the operator may have difficulty in feeling or sensing full engagement of the pawl with the fine tooth spaces.

It is the primary object of the invention to provide a detent mechanism which is simple in construction, positive in operation, and which will not require excessively close manufacturing tolerances regardless of close spacing of the positions in which the machine part is detented.

Another object is to enlarge the parts of the detent mechanism without enlarging the overall dimensions of the mechanism.

More specifically, an object is to reduce the number of detent teeth in the detent mechanism to a number less than the number of positions in which a machine part may be detented.

Other objects and advantages of the invention will be evident from the following description of a preferred embodiment thereof with reference to the accompanying drawings in which:

FIG. 1 is a side elevation of a portion of a record card sensing mechanism embodying the detent mechanism with the parts in one operated position.

FIG. 2 is an enlarged fragmentary side elevation of the detent mechanism with the parts in the operated position of FIG. 1.

FIG. 3 is a view similar to FIG. 2 with the parts in another operated position.

With reference to FIG. 1, the detent mechanism is disclosed as embodied in a perforated record card reader generally indicated by the numeral 1. The card reader employs a pair of carriages 2, one of which is shown in FIG. 1. The carriages are selectively adjustable to positions respectively corresponding to columns of the record cards to be read. The carriages respectively carry circuit control means which initiate and terminate the reading operation for each card. Accordingly, as determined by the columnar settings of the carriages, a selected field of each card is read.

The particular record cards for which the reader is designed each have eighty closely spaced columns. Therefore extremely accurate location of carriages 2 is necessary for satisfactory performance of the reader, and the 3,167,972 Patented Feb. 2, 1965 detent means of the invention has proved particularly effective for this purpose.

It will be understood that the invention resides in the detent mechanism per se, and that the card reader illustrates only an application of the invention. Therefore in the drawings only so much of the reader including a single carriage 2 is shown as is necessary to illustrate the operation of the detent means. Referenc is made to Patent 2,938,667 for a complete disclosure of the card reader.

Carriage 2 (FIG. 1) is supported for horizontal shifting movement on the framing of the reader by rollers 4. The framing of the reader includes a horizontally extending side plate 3 on which cog pulleys 5 and 6 are mounted respectively to the left and right of carriage 2. A cog belt 7 connects pulleys 5, 6 and passes adjacent the front of carriage 2.

Cog belt 7 is secured to an outwardly extending lip of an angle plate 8 which is bolted to the front of carriage 2. Cog pulley 6 is mounted for rotation with. a knob 9 which therefore may be rotated to shift carriage 2 to the right or left by movement of belt 7.

The detent means includes a longitudinal rack 10 secured in horizontal position on the outer face of plate 3, and having pointed straight sided teeth 10t disposed along its lower edge. Each tooth space 10a corresponds to two positions to which carriage 2 may be adjusted, and therefore the teeth are spaced at twice the distance of the spacing of the carriage positions as will later appear. As a result, teeth 10: may be made double the size of teeth in conventional detent means wherein each tooth space corresponds to a detent position. A suitable scale and pointer (not shown) adjustable with the carriage indicates the carriage positions corresponding to the columns of the record cards.

A pair of pawl levers 12 and 13 have common pivotal mounting 14 on the front of carriage 2 immediately below and forwardly of rack 10. A roller 12r is mounted at the end of a leftwardly extending arm of lever 12, and a roller 13r is mounted at the end of a leftwardly extending longer arm of lever 13. Levers 12 and 13 are biased clockwise by springs 15 and 16 respectively to hold rollers 12r, 13r is engagement with rack 10. The longer arm of lever 13 has a circular cut out to permit passage of roller 12r to position for engagement with rack 10. A toggle spring 18 connects the ends of depending arms of levers 12 and 13 for a purpose later described.

From an inspection of the drawings, it will be seen that rollers 12r, 13r are spaced from each other along rack 10 one and one-half tooth spaces, and that when either of the rollers engages a tooth space 10s to locate carriage 2 in a shifted position, the other roller will engage the top of a tooth 101 and will therefore be rendered ineffective.

With reference to FIG. 2, roller 13r engages a tooth space 10s to locate carriage 2, whereas roller 12r ineffectively engages the top of a tooth 10L Now if carriage 2 is shifted the distance of one half a tooth space, either to the left or right from the position of FIG. 2, roller 12r will be moved from the top of the related tooth into engagement with a next adjacent tooth space to locate the carriage in a next shifted position, as shown in FIG. 3, Whereas roller 13; will be moved from the related tooth space into engagement with the top of a next adjacent tooth. Accordingly, it will be seen that as carriage 2 is shifted to its successive positions, in either direction, it will be detented by rollers 12r and Br alternately engaging tooth spaces 10s of rack 10.

The detent mechanism operates quite satisfactorily, as described above, independently of the operation of the aforenoted toggle spring 18. Toggle spring 18, however, materially increases the eifectiveness of the detenting operation. With reference to FIG. 2, it will be seen that toggle spring 18 biases lever 13 clockwise and lever 12 counterclockwise. As a result, toggle spring 18. augments the urge of spring 16 in the detenting operation, and attenuates the now unuseful. urge of spring 15. With reference to FIG. 3, toggle spring 18 operates reversely to bias lever 12 clockwise to. increase the detenting operation and to bias lever 13 counterclockwise.

It will be noted that springs 15 and 16 are in opposition when carriage 2 is partly shiftedbetween one position and the next. However, when toggle spring 18 is carried over dead center in part movement of carriage 2 from one shifted position to the next, the shifting movement will be completed, to full detented position by action of the effective spring 15 or 16 assisted by toggle spring 18 to overcome the action of the opposed spring.

It will be understood that the principles of operation of the invention do not limit it for use with a longitudinal rack, and that the rack may be arcuate or in circular gear a rack having tooth spaces each corresponding to two of said positions;

a pair ofpawls alternately operable to engage respectively a tooth space and the top of a rack tooth upon movement of said member to its successive positions; and' means operable to urge said pawls alternately into engagement respectively with a tooth space and away from engagement with a rack tooth upon. movement of said member to its successive positions.

2. The invention according to claim 1 wherein;

said means operable to urge said pawls comprises a toggle spring connecting said pawls.

3. The combination with a member adjustable to a plurality of positions, and i means for adjusting said member;

.of detent mechanism, comprising a rack having tooth spaces each corresponding to two of said positions;

a pair of pawls alternately operable to engage respectively a tooth space and the top of a rack tooth upon movement of said member to its successive positions;

a spring. for urging each pawl into engagement with said rack; and

means operable to augment the operation of the spring of the pawl engaging a tooth space and to attenuate the operation of the spring of the pawl engaging the top of a rack tooth.

4. The invention according to claim 3 wherein;

said means for augmenting and attenuating the operation of said springs comprises a toggle spring connecting said pair ofpawls.

5. The combination with an adjustable member, and

means for adjusting said member;

of detent mechanism, comprising a rack;

a pair of pawls mounted for engaging said rack at a distance of a given number and one-half rack teeth from each other;

a spring for urging each pawl into engagement with said rack;

means for effecting movement between said rack and said pawls upon movement of said member; and

i a toggle spring connecting'said pawls and urging either pawl toward engagement with said rack when said pawl is in registration with a tooth space and urging the other pawl away from said rack.

References Cited in the file of this patent UNITED. STATES PATENTS 

1. THE COMBINATION WITH AN ADJUSTABLE MEMBER, AND MEANS FOR ADJUSTING SAID MEMBER TO A SUCCESSION OF POSITIONS; OF A DETENT MECHANISM, COMPRISING A RACK HAVING TOOTH SPACES EACH CORRESPONDING TO TWO OF SAID POSITIONS; A PAIR OF PAWLS ALTERNATELY OPERABLE TO ENGAGE RESPECTIVELY A TOOTH SPACE AND THE TOP OF A RACK TOOTH UPON MOVEMENT OF SAID MEMBER TO ITS SUCCESSIVE POSITIONS; AND MEANS OPERABLE TO URGE SAID PAWLS ALTERNATELY INTO ENGAGEMENT RESPECTIVELY WITH A TOOTH SPACE AND AWAY FROM ENGAGEMENT WITH A RACK TOOTH UPON MOVEMENT OF SAID MEMBER TO ITS SUCCESSIVE POSITIONS. 